Don't bother with another 7.5" rear. Go with a good 8.8 so you don't have the troubles, again. The 8.8 just has a MUCH better bearing design, stronger crosspin (which is what you snapped in half), etc. Find you any 1999-2004 V8 Mustang in the junk yard and take the rear axle. Check out www.car-part.com
and see if you can find one local to you. I would really recommend you not waste your time on another 7.5. The 8.8 will bolt directly in its place.